Spray a baking sheet with non-stick spray. Shape the meat into four oval shaped patties, place on the pan and put into the freezer for 15 minutes.
Meanwhile, heat the oil and butter in a cast iron skillet. Add the onion and cook over medium high, stirring regularly, for about 5 minutes or until softened. Reduce heat to medium and continue cooking, stirring regularly, until caramelized, about 15-20 minutes. Use a slotted spoon to remove the onion; set aside.
Sprinkle the meat patties with the garlic salt and pepper. Place into the same skillet, seasoning side down, and turn the heat back up to medium high. Cook until the patties are well browned on the underside, and mostly cooked through. Flip, scatter onions on top and place a slice of cheese on top of the onions. Cover with a lid and move off of the heat source to let the cast iron finish cooking through. If you are not using cast iron, you'll need to keep the burgers over direct heat until cooked through.
Generously butter one side of all of the bread slices. Place, butter side down into a fresh large non-stick skillet and place a slice of cheese on top of each slice of bread. Cook the bread until well browned on the underside. Top each bread slice with one of the meat patties and add some of the dressing. Top with a slice of buttered bread, butter side out, and carefully turn over to brown the other side, gently pressing down. Cook until well browned, transfer to serving plates and cut
1-1/2 pounds of ground chuck
1 large Vidalia or yellow onion, chopped
1 tablespoon of canola or vegetable oil
1 tablespoon of unsalted butter, plus additional softened butter for the bread slices
4 slices of Swiss cheese
8 slices of rye bread
Garlic salt and freshly cracked black pepper, to taste
Thousand Island Dressing